Natural rubber obtained from plant life is the preferred source of cis-1,4-polyisoprene. Among the many advantages of natural rubber are its relatively inexpensive cost, its high wet gel strength, and its ability to rapidly cure.
Many of the products derived from natural rubber, especially dip-formed goods such as gloves, condoms, and tubing, typically come into contact with the user for extended periods of time. This contact is not only experienced through the skin, but is also experienced as a result of air-borne particles that enter the respiratory system. As a result of such exposure, many people have developed a hypersensitivity to natural rubber. This hypersensitivity includes Type I allergenicity, which affects approximately 6.5 percent of the U.S. population
It is believed that natural rubber allergenicity results from the proteins and/or inorganic salts that are found within naturally occurring rubber latex. The proteins found within latex are both soluble and insoluble in aqueous mediums, and can be bound to the surface of the rubber particles or are associated with organelles. For example, the major source of natural rubber is the Hevea brasiliensis tropical tree which naturally produces rubber latex comprising globules of polyisoprene coated with proteins suspended in an aqueous dispersion. This dispersion comprises about 60 to about 75 percent water, about 25 to about 40 percent polyisoprene, about 1 to about 2 percent protein, and a balance of sugars and inorganic salts.
Another viable commercial source of natural rubber exists in the guayule shrub, which is native to North America. Like the Hevea rubber tree, the guayule shrub naturally produces cis-1,4-polyisoprene in a latex. Unlike Hevea, however, where access to the latex is achieved by merely tapping the tree, the latex within guayule is typically separated by crushing the entire plant because of the size of the plant and the position of the rubber within the plant.
Surprisingly, it has been recently found that the naturally occurring latex of the guayule bush does not elicit Hevea allergic responses. Thus, rubber allergenicity is believed to be species specific. In fact, recent analytical data confirms that many of the Hevea antigens believed to elicit Hevea allergenicity are not found in naturally occurring guayule latex. Accordingly, it is believed that Hevea latex allergy can be circumvented by using rubber from other species.
Nonetheless, it has recently been found, however, that latex obtained from guayule contains antigens that are capable of inducing immune responses distinct from those reactions with Hevea antigens. As a result, the proteins found within guayule latex must be considered potentially allergenic. It is hypothesized that naturally occurring latex from other plant life sources may also contain proteins that may elicit immune responses.
Thus, a need exists to develop a natural rubber latex that is essentially devoid of proteins that are known to elicit Hevea allergenic responses, or proteins found in guayule that are believed to elicit immune responses.